Witcher gear has a number of tiers from Basic, Enhanced, Mastercrafted and Superior. Each item in a Witcher set, for each tier requires you to find the diagram.
In most cases you'll need to find maps from merchants and in chests which will start Treasure Hunt quests which allow you to track down the various diagrams you'll need to complete your set.
I found all of the Superior Ursine diagrams in a chest in a cave, but I do not recall where. However I don't have any other versions, and it's also worth noting I did not have any previous Ursine set diagrams.
The location appears to be in the monster den North West of the Hanged Mans Tree.
So in total, to get your Superior Ursine set, you'll need to have found 6 diagrams 4 times, so you'll need 24 diagrams in total to complete the whole set to Superior quality, including the swords.
The other thing that's worth checking is that you might have the diagrams, but your crafting filter might be omitting them from the list. Also be sure to visit a master Armourer, as the filter can omit diagrams for craftsmen who's level is not high enough.